Method and device for the protection of the refractory masonries



G. CONQS'OGNO May 27, 1969 METHOD AND DEVICE FOR THE PROTECTION OF THEREFRACTORY MASQNRIES Sheet I z of 3 Filed Feb. 27. 1967 y 7, 1969 ca.CONSOGNO 3,446,494

METHOD AND DEVICE FOR THE PROTECTION OF THE REFRACTORY MASONRIES Sheet Zof 3 Filed Feb. 27, 1967 FIG. 3

FIG.4

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y 27, 1969 G. CONSOGNO 3,446,494 I METHOD AND DEVICE FOR THE PROTECTIONOF THE REFRACTORY MASONRIES Filed Feb. 27, 1967 Sheet 3 of 5 FIG.8

United States Patent U.S. Cl. 263-44 14 Claims ABSTRACT OF THEDISCLOSURE The invention relates to method and apparatus for theprotection of refractory masonries and in particular the crowns of openhearth furnaces. In accordance with the invention, nitrogen isinsulflated under pressure against the furnace crown so that between thecrown itself and the atmosphere of the furnace there is formed a cushionof nitrogen under pressure which is continuously renewed. Preferably,the nitrogen is introduced under pressure in a direction substantiallytangent to the crown to be protected. The pressure of the nitrogeninsufllation is preferably kept between 4 and 12 atmospheres and thenitrogen delivery is controlled so that its cooling action on themasonries to be protected keeps the masonries at a selected temperaturewhich may, for example, vary between 1,400 C. and 1,600 C.

Apparatus for carrying out the method comprises a set of nozzles forblowing the nitrogen under pressure just under the crown of an openhearth furnace through a series of blowing heads fed through suitableconduits. Each blowing head is preferably provided with a set of nozzlesand axial conduit for supplying cooling liquid under pressure, an outerjacket providing an annular ai cavity for return of the cooling liquidand a cylindrical chamber placed at the end of the head to receive thecooling liquid. A suitable set of conduits puts the chamber incommunication with the lower zone of the annular air cavity. The nozzlesfor the nitrogen are preferably radially disposed in a sector of theblowing head.

Object of the present invention is the utilization of an inert gas toprotect the inner walls of the crowns in the open hearth furnaces andthe cooled lance by means of Which the maintenance of the defensiveshield is possible.

The recently developed technique of the direct insufflation of oxygenduring the steel refining process, has the serious disadvantage ofcausing an excessive wearing to the refractory material of the crownswith consequent shorter life of the furnace life.

Object of the invention is to prevent this disadvantage in order toextend the life of the refractory material by keeping it out of directcontact and by diluting the con centration of the oxygen in excess inthe laboratory atmosphere.

Besides a purely chemical protection effect, object of the presentinvention is to protect mechanically the refractory crown of the furnaceagainst the bath sprinkles and the powders dragged by the fumes, and toobtain, by means of nitrogen, a cooling effect which reduces the thermalstress of the refractory materials.

The method for the protection of the refractory masonries, particularlyof the crowns, in the open hearth furnaces, is characterized in that itprovides the insufllation of nitrogen under pressure towards the furnacecrown, so that a cushion of nitrogen under pressure continuously renewedis formed between the crown itself and the furnace atmosphere, thiscushion finds its way out from the furnace also through the intersticesexisting among the bricks.

The insufllation of nitrogen is effected right under the furnace crown,by means of blasts of nitrogen under pressure, the axis of which ispreferably substantially tangent to the crown to be protected, so thatthe insufllated nitrogen expands tangentially to the crown to beprotected, remaining adjacent to it, without being violently reflectedagainst the surface of the underlaying bath. The nitrogen insufliationpressure is preferably kept between 4 and 12 atmospheres.

The nitrogen delivery is arranged in function of the delivery of oxygeninsufilated against the bath surface.

At present, according to the necessity, from 1,400+ 1,800 Nmc/h (cubicmeters of nitrogen per hour) of oxygen are blown in.

The range may vary in the time according to the availability of 0 Aminimum constant nitrogen delivery of about Nmc/h. 200 is provided. Uponthe insufllation of 0 said delivery should vary between 300 and 500Nmc/h. (maximum availability of nitrogen in the present equipmentconditions).

Consequently it is possible in the future to vary, according to theavailability, the delivery of both fluids in order to speed up thecharge refining times.

The delivery of nitrogen is controlled in a different solution so thatits cooling action on the masonries to be protected keeps them at atemperature lower than a prefixed one.

In function of the crown temperature with a lance considered for adelivery of 10 atm. of nitrogen, the following value range will be used:

Degrees C.: Delivery Nmc./h.

The equipment for embodying the above process is characterized in thatit comprises a set of nozzles, for blowing nitrogen under pressure,suitably placed just under the crown of an open hearth furnace, througha series of blowmg heads fed through suitable conduits preferablycrossing the crown itself.

The cited nozzles have their axis substantially parallel to the furnacecrown or anyhow slightly inclined towards the crown.

Each blowing head is provided with a set of nozzles distributedaccording to a sector of suitable width.

Each blowing head is provided with an axial conduit for the supply of acooling liquid under pressure, like water; an outer jacket providing anannular air cavity for the return of the cooling liquid; a cylindricalchamber placed correspondingly to the end of the cited head, into whichthe cooling liquid flows; a suitable set of conduits puts the saidchamber in communication with the lower zone of the cited annular aircavity; at least a conduit for the supply of the nitrogen underpressure, comprised between the cited axial conduit and the citedannular air cavity; a series of radial nozzles distributed according toa sector of suitable width, with their axes substantially perpendicularto the axis of the cited head, said nozzles putting into communicationthe lower end of the inflow conduit of nitrogen with the outer part ofthe cited head.

Right above the port of the nitrogen outlet nozzles, the cited blowinghead is provided with a sharp constriction so as to have a free surfacefor the nitrogen flow obtained over said nozzles. Also the length anddiameter of each nozzle can be varied as a function of the feedingpressure of the nitrogen, in this way the outer diameter of the lance isvaried accordingly.

The objects, advantages and characteristics of the invention willfurther result from the following description, referring to embodimentschosen by way of example only with reference to the accompanyingdrawings, wherein:

FIG. 1 shows the plan from the bottom of the standard crown of an openhearth furnace; FIG. 2 shows the same crown in the same projectionillustrated in FIG. 1, the positions of the lances for nitrogen blowingand further the direction to which the relative nozzles must bearranged; FIGS. 3 and 4 show in section, according to a horizontal planeand a vertical one respectively, the distribution area of a flow ofnitrogen coming out from a nozzle at a pressure of 8 atm.; FIGS. 5 and 6are similar to the preceding FIGURES 3 and 4, in the case the nitrogenfeeding pressure is at atm.; said diagrams have been obtainedexperimentally; FIG. 7 is a plan from above of a head for blowingnitrogen under pressure; in a preferred embodiment; FIG. 8 is a sectionaccording to the lines VIII-VIII of the preceding FIG. 7.

With particular reference to FIGS. 1 and 2: 1 is the section of the planfrom above of the standard crown of an open hearth furnace; the dottedline 2 is the outline of the zone 3 of greater wearing of the furnacecrown; 4 are the holes through which pass the lances for blowing oxygenunder pressure, the position thereof being directly connected with theextension of the zone 3; 5, 6, 7 and 8 are the positions of four headsfor blowing nitrogen under pressure; while the heads for the lances forblowing oxygen project under the furnace crown towards the bath surface,the heads 5 to 8 for blowing nitrogen are practically adjacent to thelower surface of the furnace crown; the curves 9 to 12 are the areas forthe distribution of the nitrogen coming out from the heads 5 to 8respectively, when it is fed at the pressure of 12 atmospheres; thecurves 13 to 16, similar to the preceding ones, refer to the case whenthe nitrogen is fed at a pressure of 10 atmospheres; the arrows 17 to 20are the intermediate positions to which the sets of nozzles of theoutflow heads 5 to 8 are directed.

As clearly seen in FIG. 2, the zone 3 limited by the dotted line 2 issubstantially wholly covered by the distribution area of the nitrogenflow coming out from the set of nozzles which each outflow head 5 to 8is provided with; in the vertical sense, said area of nitrogendistribution has the course indicated in FIGS. 4 to 6; that is, thenitrogen is practically directed to a direction tangential to thefurnace crown, so that a protecting cushion is formed between the crownand the underlaying laboratory atmosphere, said cushion however, doesnot mix with said underlying atmosphere and therefore it does notinterfere with the flow of oxygen coming out from the correspondinglance at a lower level. Consequently, the effectiveness of the oxygenaction is not reduced by the presence of the outflow of nitrogen.

With particular reference to FIGS. 3 to 6, the values denoted on theaxis of the abscissas and of the ordinates of the four diagramsillustrated in FIGS. 3 to 6, are, in millimetres, the distances in thetwo orthogonal directions, from the centre of a generic inflow head forthe nitrogen; as indicated in FIGS. 4 to 6, at a distance of about 4metres from the corresponding outflow head, the thickness of the outflowarea of nitrogen, measured in a vertical sense, is till lower than 500mm., which assures both the eificiency of a nitrogen cushionsufliciently compact and the non-interference with the underlyingoutflow Zone of the oxygen.

Anyhow, the distribution areas of the nitrogen outflow may he obviouslymodified each time by acting, according to the necessities, on thenumber of nozzles provided in each head, on their diameter and shape, onthe feeding pressure, on the distribution of the nitrogen outflow headsand the like.

With particular reference to FIGS. 7 and 8: the outfiow head 21comprises substantially two cylindrical bodies 22 and 23 coaxial andoverlapped, the side surfaces of which are connected by means of acone-shaped surface 24; on the cylindrical surface 22, right under thesurface 24, the outflow nozzles 25 for the nitrogen are placed; as shownin FIG. 8 the nozzles 25 have their axes 26 substantially horizontal; asshown in FIG. 7, the axes of the set of nozzles of each head 21 areplaced radially wtih respect to the axis of head 21 and they aresubstantially distributed in a single practically horizontal plane; theseries of nozzles 25 embraces a sector which, in the shown preferredcase, corresponds to about in such a way, the four outflow heads 5 to 8can cover with the nitrogen flow the whole zone 3 as shown in MG. 2; itis obvious that, with a different distribution of the outflow heads, thecited angle could be different from 90 as indicated in the figure.

Each one of the heads 21 is provided with a central conduit 27 for theinflow of a cooling liquid constituted, for instance, by water; saidconduit flows into a cylindrical cavity 28 and herefrom, through a setof inclined ducts 29, reaches an air cavity 30 constituting the backduct of the cited cooling liquid; 31 is a duct asymmetric with respectto the axis of the lance 21 necessary for carrying the nitrogen underpressure and ending correspondingly to the inflow inlet of the nozzles25.

As already said, the delivery of nitrogen may be regulated according tothe temperature of the furnace crown, so that said temperature is alwayskept under a prefixed value; said delivery may also be regulated infunction with the delivery of oxygen insufflated into the furnace, beingthe quantity of insufflated oxygen the governing factor on which thecrown temperature depends.

In the first case the valve which regulates the delivery of nitrogenwill be directed through one or more thermocouples measuring constantlythe temperature of the furnace crown; in the second case said valve willbe suitably coupled with the valve which regulates the oxygen delivery,so that the deliveries of the two gaseous fluids are therebetweenarranged according to the values of a prefixed ratio possibly variableaccording to a prefixed rule.

Although for describing reasons, the present invention has been based onthat described and illustrated above by way of example only, manymodifications and variations may be made in embodying the invention.

I claim:

1. A method for the protection of the refractory masonry, andparticularly the crown of a furnace in which steel is refined byinsufliation of oxygen, which comprises blowing nitrogen under pressurealong the lower face of the furnace crown and substantially tangentiallythereto, to form a cushion of nitrogen between said crown and theatmosphere of said furnace, permitting said nitrogen to exit from saidfurnace and through the interstices existing in the furnace masonry, andcontinuously renewing said cushion of nitrogen.

2. A method according to claim 1 in which said nitrogen is blowndirectly under said furnace crown by means of blasts of pressurizednitrogen which have axes substantially tangent to said crown wherebysaid nitrogen expands tangentially to said crown, and remains adjacentthereto without being violently reflected against the surface of theunderlying bath contained in said furnace.

3. A method according to claim 1 in whcih said nitrogen is blown under apressure of 4 to 12 atmospheres.

4. A method according to claim 1 in which the amount of nitrogen blowninto said furnace is adjusted as a function of the amount of oxygenblown into said furnace, and in which oxygen is blown into said furnacein an amount of about 1,400 to 1,800 times the amount nitrogen blowninto said furnace.

5. A method according to claim 4 in which the amount of said nitrogenblown into said furnace is about 300 to 500 cubic meters per hour.

6. A method according to claim 1 in which said nitrogen is cooled priorto its entry into said furnace.

7. A method according to claim 1 in which the amount of said nitrogenblown into said furnace is adjusted so as to maintain said masonriesbeing protected under a predetermined temperature and in which at acrown temperature of l,400 to 1,600 C. the amount of nitrogen blown intosaid furnace is from about 200 to 400 cubic meters per hour while thefeeding pressure of said nitrogen correspondingly varies from about 4 toabout 12 atmospheres.

8. In a furnace for refining steel by insufllation of oxygen, a crownand means for protecting said crown from the atmosphere and bath of thefurnace and also from heat, said means comprising a series of blowingheads fed through ducts in said crown and a set of nozzles in saidblowing heads for blowing nitrogen just under said crown.

9. A furnace according to claim 8 in which said furnace is anopen-hearth furnace.

10. A furnace according to claim 8 in which said nozzles have axes whichare substantially parallel to or slightly inclined toward said crown.

11. A furnace according to claim 8 in which a series of said nozzles isdistributed along a sector of each of said blowing heads, in which theaxes of said nozzles are parallel to or slightly inclined toward saidcrown and in which said blowing heads are positioned across said crownso that nitrogen flowing through said nozzles forms a cushion ofnitrogen just under the lower face of said crown.

12. A furnace according to claim 8 in which each blowing head isprovided with a duct for the inflow of cooling fluid, a chamber incommunication with said duct for the inflow of cooling fluid andpositioned at the end of said blowing head which projects farthest intosaid furnace and means for the return of said cooling fluid from saidchamber.

13. A furnace according to claim 8 in whicheach blowing head is providedwith an axial duct for the inflow of cooling fluid, a fluid chamber incommunication with said axial duct and positioned at the end of saidblowing head which projects farthest into said furnace, an outer jacketcreating an annular air cavity for the return of said cooling fluids,ducts in communication with said fluid chamber and said outer jacket,and at least one duct for the inflow of pressurized nitrogen incommunication with said nozzles and positioned between said axial ductand said outer jacket.

14. A furnace according to claim 8 in which the outer surface of saidblowing head is provided with a sharp constriction above the outlet ofsaid nozzles so as to have a free surface for forming the flow ofnitrogen above said nozzles and in which said nozzles are variable inlength and diameter.

References Cited UNITED STATES PATENTS 1,665,205 4/1928 Getz 263441,783,284 12/1930 Easter 26344 2,186,740 1/1940 Teeters 26344 2,293,3328/1942 Dow et a1. 26344 X 3,165,301 1/1965 Riviere 26315 JOHN J. CAMBY,Primary Examiner.

Us. 01. X.R-. 266 -33

